1. Field
The present subject technology relates to telecommunications and more particularly to controlling or administering access to a telecommunications channel for a subscriber station.
2. Background
This Background and discussion of related art is presented with benefit of hindsight and knowledge of the inventive concepts discussed throughout this document, and therefore none of this discussion or any of the referenced mentioned herein is admitted prior art.
Universal Mobile Telecommunications System (UMTS) is one of the third generation (3G) mobile telephone technologies (or 3rd Generation Wireless Mobile Communication Technology). A UMTS network consists of 1) a Core Network (CN), 2) a UMTS Terrestrial Radio Access Network (UTRAN) and 3) User Equipment (UE, also known as a “mobile” or “mobile unit”), also known as a mobile station. The core network provides routing, switching, and transit for user traffic. A Global System for Mobile Communications (GSM) network with General Packet Radio Service (GPRS) is the basic core network architecture that UMTS is based on. The UTRAN provides the air interface access method for User Equipment. A base station is referred to as Node B and control equipment for Node Bs is called a Radio Network Controller (RNC). For an air interface, UMTS most commonly uses a wideband spread-spectrum mobile air interface known as Wideband Code Division Multiple Access (or W-CDMA). W-CDMA uses a direct sequence code division multiple access signaling method (or CDMA) to separate users.
A UMTS Terrestrial Radio Access Network (UTRAN) is a collective term for the Node Bs (or base stations) and the control equipment for the Node Bs (or RNC) it contains which make up the UMTS radio access network. This is a 3G communications network which can carry both real-time circuit switched and IP based packet switched traffic types. The RNC provides control functionalities for one or more Node Bs. Connectivity is provided between the UE (user equipment) and the CN (core network) by the UTRAN.
The UTRAN is connected internally or externally to other functional entities by four interfaces: Iu, Uu, Iub and Iur. The UTRAN is attached to a GSM core network via an external interface called Iu. A radio network controller (RNC) supports this interface. In addition, RNC manages a set of base stations called Node Bs through interfaces labeled Iub. The Iur interface connects two RNCs with each other. The UTRAN is largely autonomous from the core network since the RNCs are interconnected by the Iur interface. FIG. 8 discloses a communication system which uses the RNC, the Node Bs and the Iu and Uu interfaces. The Uu is also external and connects the Node B with the UE, while the Iub is an internal interface connecting the RNC with the Node B.
The RNC fills multiple roles. First, it may control the admission of new mobiles or services attempting to use the Node B. Second, from the Node B, i.e. base station, point of view, the RNC is a controlling RNC. Controlling admission ensures that mobiles are allocated radio resources (bandwidth and signal/noise ratio) up to what the network has available. It is where Node B's Iub interface terminates. From the UE, i.e. mobile, point of view, the RNC acts as a serving RNC in which it terminates the mobile's link layer communications. From the core network point of view, the serving RNC terminates the Iu for the UE. The serving RNC also controls the admission of new mobiles or services attempting to use the core network over its Iu interface.
In the UMTS system, universal terrestrial radio access (UTRA) frequency division duplex (FDD) channels and UTRA time division duplex (TDD) channels may be used to communicate data. The communication link through which the user equipment sends signals to the Node B is called a uplink.
Users may attempt to access a telecommunications network, such as a cellular network, by using a cellular telephone or other user equipment to place a call. For example, a user may enter a telephone number into the mobile unit and press a “Send” key. One of the first steps in handling the call is to determine whether the call is being placed to emergency services, or is otherwise to be assigned a special “access services code” or “access service class” (interchangeable terms that are both abbreviated “ASC”). If the attempted access appears to be directed to emergency services, such as a call to “911” in the United States or a call to “112” in Europe, then the user equipment may determine an ASC=0, which indicates that the call is to be given the highest priority. Generally, if the call is not being directed to emergency services and is not being placed by a member of the emergency services, then the user equipment assigns the call an ASC=1, although in some situations other access service codes may be used. For example, the 3GPP specification allows a cellular operator to allow user equipment to determine an ASC of any integer value from zero to seven, although most cellular operators implement their networks using only ASC=0 and ASC=1.
If ASC=0, then the user equipment immediately attempts to pass the call through to the communications network. If ASC=1, however, then the user equipment calculates a “persistence” value based on previous base station transmissions, and iterates through a loop. Each iteration, the user equipment generates a random number and only allows the access attempt if the random number is less than the persistence value. The persistence value may be regarded as a probability that the user equipment will connect to the network during each iteration.
By providing immediate access to all access attempts for which ASC=0, the cellular network can give priority to emergency calls, such as call to 911 in the United States. Emergency calls may be said to have a 100% persistence value, in that the user equipment will certainly initiate the access attempt immediately. When only a few users are placing calls to emergency services, this technique works well. However, if too many users attempt to call emergency services simultaneously, congestion may result in collisions. For example, if a large-scale disaster or similar emergency occurs, very large numbers of people may attempt to place calls to emergency services. Since all such calls are given immediate access, network congestion will result, and none of the calls will gain access to the cellular network. Without any randomization there is the potential for a high level of collisions among mobile stations trying to place emergency calls all at the same time. If all of the users retry their calls after failing to receive an acknowledgement, another collision will result, and none of the users will gain access to the telecommunications network; all calls will again attempt to gain access to the cellular network, and all will again fail. The situation will result in repeated attempts indefinitely, with no success.